The Ishtar Terra highland region of Venus contains mountain belts morphologically similar to terrestrial orogenic belts. Akna Montes and Freyja Montes are long, linear mountain belts with about 4 km of relief above the 3- to 4-km-high Lakshmi Planum. The Maxwell Montes mountain belt, however, is more rectangular in plan view and has relief of approximately 8 km. We have investigated the natue of this latter range using complementary radar images obtained by the Arecibo Observatory and the Venera 15/16 spacecraft, as well as altimetry data obtained by the Venera 15/16 and Pioneer Venus spacecraft. Geological and structural maps have been compiled on the basis of these data, the individual features and their stratigraphic relationships interpreted, and a model for the origin and evolution of Maxwell Montes is proposed. The dominant features of this mountain range are long, parallel ridges and valleys that are interpreted to be anticlines and synclines and to have resulted from ENE-WSW oriented compression. Two major shear zones bound Maxwell Montes on the north and south, converging toward the west. Nine narrow linear parallel features several hundreds of kilometers long (identified as cross-strike discontinuities, CSDs) cut obliquely across the strike of the ridges and valleys in a NW-SE direction and disrupt the structural fabric of the mountain range, dividing Maxwell Montes into 10 crustal domains.

Among several possible origins, we find that the data are most consistent with their interpretation as right-lateral strike-slip faults with offsets of up to 125 km. Retrodeformation and reconstruction of Maxwell Montes using the offsets determined for individual domains produces a long linear mountain range similar to Akna Montes. Using geologic unit maps and topographic maps of the present configuration of Maxwell, similar reconstructions were made; these reconstructions restored several linear tectonic elements, topographic trends, and sinuous unit boundaries to more contiguous positions. On the basis of these data and observations we suggest that Akna Montes may represent the initial form of compressional orogenic belts on Venus, while Maxwell Montes attained its present morphology through a second stage of deformation involving large-scale strike-slip faulting. We examine several models for this second stage and favor the interpretation that it occurred as the Akna Montes-like proto-Maxwell Montes was transported to the west between two converging shear zones, accompanied by rotation of the entire mountain range. Thirty percent shortening of the mountain range is implied by the geometries of the present and reconstructed Maxwell Montes. On the basis of the deformation in Maxwell Montes and the evidence for large-scale transport we conclude that large-scale horizontal movement of crustal material is a significant aspect of the tectonics of Venus. ¿ American Geophysical Union 1990